Prior known examples of the above ozone treatment apparatus include the ashing apparatus disclosed in Japanese Unexamined Patent Publication No. 5-166718. As shown in FIG. 3, the ashing apparatus 100 comprises a placement table 101 on the upper surface of which a wafer W is placed, a transparent quartz plate 102 disposed above the wafer W by being spaced a prescribed distance g away from the surface of the wafer W, a nozzle 103 disposed with its one end opening in the surface of the quartz plate 102 that faces the wafer W, and a plurality of UV lamps 104 arranged above the quartz plate 102.
The placement table 101, the quartz plate 102, the nozzle 103, and the UV lamps 104 are arranged inside a chamber (not shown) having a closed space. The placement table 101 contains a heater 105, and the nozzle 103 is connected to an ozone gas generating apparatus (not shown).
According to the thus constructed ashing apparatus 100, the wafer W placed on the upper surface of the placement table 101 is heated to a predetermined temperature by the heater 105, and an ozone gas (treatment gas) of predetermined concentration generated by the ozone gas generating apparatus (not shown) is discharged from the nozzle 103 toward the heated wafer W.
The thus discharged ozone gas impinges on the wafer W and forms an ozone gas layer flowing along the surface thereof, while being exposed to UV rays from the UV lamps 104. While the gas is flowing, the ozone (O3) is heated by the wafer W and, by thus being heated and contacting the wafer W and resist, or by being exposed to UV rays from the UV lamps 104, the ozone is decomposed into oxygen (O2) and active oxygen (O*), and the resist film formed on the surface of the wafer W is removed by thermochemical reaction with the active oxygen.
Here, the quartz plate 102 is provided to control the flow velocity of the ozone gas stream flowing along the surface of the wafer W; that is, when the spacing g with respect to the wafer W is reduced, the layer thickness of the ozone gas stream decreases and the flow velocity increases, so that the surface of the wafer W, even portions thereof farther from the nozzle 103, can be treated efficiently, that is, the surface area that can be treated increases.
On the other hand, when the spacing g is increased, the layer thickness of the ozone gas stream increases and the flow velocity decreases, as a result of which portions farther from the nozzle 103 may remain untreated, that is, the surface area of the wafer W that can be treated decreases.
Accordingly, it is preferable to set the spacing g as small as possible so that the treatment can be performed efficiently over the large surface area.
However, when the flow velocity of the ozone gas stream is increased by decreasing the spacing g, if this condition is maintained for more than a certain length of time, the portion directly below the nozzle 103 and its neighboring portions on the surface of the wafer W are cooled by the high-velocity ozone gas stream, and its surface temperature drops, suppressing the ozone gas decomposition on the affected portions. This has resulted in uneven treatment or no treatment of the cooled surface portions of the wafer W. If the occurrence of such unevenly treated or untreated portions is to be prevented, it has been necessary to perform the treatment for an extended period of time.
The present invention has been devised in view of the above situation, and an object of the invention is to provide an ozone treatment method and an ozone treatment apparatus that can uniformly treat the substrate surface in a short time.